The invention relates to a colour display tube which comprises a display window, a system for emitting an emission pattern of juxtaposed rows of electron beams, a deflection system between the emission system and the display window for deflecting the electron beams, comprising deflection electrodes extending between adjacent rows of the emission pattern, and a phosphor pattern provided on the display window and correlated with the emission pattern.
A colour display tube of the type described in the opening paragraph is known from U.S. Pat. No. 4,404,493. In this Specification a colour display tube is described which comprises a number of parallel wire cathodes in a vacuum envelope. By selectivity switching on and off the wire electrodes a line of the picture can be built up. The emission system further comprises, a pair of parallel plate electrodes situated in front of the wire cathodes and provided with rows of apertures aligned with the wire cathodes. A system of flat strip-shaped electrodes extending transversely to the wire cathodes are present between the plate electrodes. The width of these electrodes corresponds approximately to the distance between adjacent apertures in a plate electrode. The strip-shaped electrodes are also provided with apertures aligned with the wire cathodes. The three electrodes constitute an array of aligned triplets of apertures consisting of one aperture in one of the plate electrodes, one aperture in a strip electrode and one aperture in the other plate electrode. During operation, this emission system emits electron beams in an emission pattern of juxtaposed rows, in this example parallel rows. Potential differences between the plate electrodes and the strip-shaped electrodes are controlled as a function of time in cooperation with the selective switching on and off of the wire cathodes so that an electron beam is emitted selectively in a number of points of a row. An array of parallel strip-shaped deflection electrodes are present between the emission system and the display window, alternate ones being a first group of commonlhy connected electrodes, and the remaining ones being second commonly connected electrodes. A phosphor pattern built up from sub-patterns in the colours red, green and blue is present on the display window. The phosphor pattern is correlated with the emission pattern. By applying potential differences between the groups of deflection electrodes, the electron beams are deflected towards the sub-patterns. As a result of this it is possible to construct a colour picture.
A disadvantage of the known colour display tube is that very high requirements are imposed upon the correlation between the emission pattern and the phosphor pattern. Since the pattern comprises juxtaposed rows, the phosphor pattern generally comprises juxtaposed triplets of rows or lines. The phosphor pattern may be unintentionally shifted with respect to a desired position during manufacture of the display tube. In the known construction it is not possible to correct the results of a shift transversely to the rows of the phosphor pattern in a simple manner.